1. Field of the Invention
The present invention relates to a control device of an internal combustion engine including a first fuel injection mechanism (i.e., in-cylinder injector) for injecting fuel into a cylinder and a second fuel injection mechanism (i.e., intake manifold injector) for injecting fuel into an intake manifold or an intake port, and particularly to a technique suppressing dilution of a lubricating oil of the internal combustion engine with fuel injected from the first fuel injection mechanism.
2. Description of the Background Art
A certain kind of known internal combustion engine includes an intake manifold injector for injecting fuel into an intake manifold of an engine and an in-cylinder injector for always injecting the fuel into a combustion chamber of the engine, and is configured such that the intake manifold injector stops the fuel injection when an engine load is lower than a predetermined set load, and injects the fuel when the engine load is higher than the set load. In this internal combustion engine, a total injection amount, which is a sum of amounts of the fuel injected from both injectors, is predetermined as a function of the engine load, and increases with the engine load.
The in-cylinder injector has a hole directly opening to a combustion chamber of the internal combustion engine, and injects fuel, which is pressurized by a fuel pump, directly into the cylinder. The in-cylinder injector directly injecting the fuel into the cylinder of the internal combustion engine performs the fuel injection in a later stage of a compression strike to control precisely a mixture state of an air-fuel mixture in the cylinder for improving fuel consumption and others. However, the in-cylinder injector may cause the following disadvantage during a cold state of the engine because it directly injects the fuel into the cylinder.
In the cold state of the engine, atomization of the fuel in the cylinder is relatively suppressed, and a large amount of injected fuel is liable to adhere to a top surface of a piston and an inner peripheral surface of the cylinder. During the cold state of the engine, therefore, such setting is employed that the fuel injection is performed in the intake stroke (i.e., the intake stroke injection is performed) to increase a period from the fuel injection to the ignition as long as possible for promoting atomization of the injected fuel. However, even this intake stroke injection cannot completely prevent the foregoing fuel adhesion, and a part of the fuel will remain in the adhering state within the cylinder after the combustion without being burned.
A part of the fuel adhered to the piston top surface is gradually atomized, and will be discharged from the cylinder after incomplete burning in the next combustion stroke. This causes occurrence of black smoke, increase in unburned components and others, and thus impairs the emission characteristics.
A part of the adhering fuel, and particularly the fuel adhering to the inner peripheral surface of the cylinder is mixed with a lubricating oil, which adheres to the inner peripheral surface of the cylinder for lubricating the piston of the engine. Therefore, the fuel dilutes the lubricating oil, and thus a so-called fuel-dilution occurs. The lubricating oil thus diluted with the fuel in the cylinder is scraped off by the vertically moving piston. The lubricating oil thus scraped returns to an oil pan, and will be reused for lubricating the engine. If the fuel frequently dilutes the lubricating oil, a rate of the mixed fuel with respect to the whole lubricating oil gradually increases, and this will cause adverse effects on the lubricating performance of the internal combustion engine such as lowering of the lubricating performance.
Japanese Patent Laying-Open No. 2003-322044 has disclosed a fuel injection control device of an internal combustion engine of an in-cylinder injection type. This control device flexibly controls a manner of fuel injection according to an actual extent of the adverse effect, which is exerted on the internal combustion engine by deterioration of emission characteristics due to adhesion of fuel to a top surface of a piston and an inner peripheral surface of a cylinder.
This fuel injection control device is used in the internal combustion engine of the in-cylinder injection type configured to inject the fuel directly into the cylinder of the internal combustion engine, and includes a dilution degree estimating unit estimating the degree of dilution of a whole lubricating oil, which is used for lubricating the internal combustion engine, with the fuel, and a control unit controlling a fuel injection manner to suppress dilution of the lubricating oil with the fuel when an estimated degree of dilution with the fuel is large.
According to this fuel injection control device of the internal combustion engine of the in-cylinder injection type, when the whole lubricating oil is diluted with the fuel only to a small extent, the fuel injection is temporarily allowed even in such a situation that fuel injection is performed under in a situation that the fuel adhering to the inner peripheral surface of the cylinder increases in amount to increase the extent of fuel-dilution (i.e., dilution with fuel). This can suppress the adhesion of the fuel to the top surface of the piston, and thereby can suppress deterioration of the emission characteristics such as occurrence of black smoke as far as possible. Conversely, when the degree of fuel-dilution of the whole lubricating oil increases to such an extent that further fuel-dilution will cause unignorable adverse effects such as lowering of the lubrication performance, the fuel injection is controlled to suppress the dilution of the lubricating oil with the fuel. Consequently, it is possible to suppress the adverse effects due to the fuel-dilution of the lubricating oil.
However, if the fuel injection manner or form (specifically, a fuel injection time of the in-cylinder injector and a fuel pressure) is changed as disclosed in Japanese Patent Laying-Open No. 2003-322044, it may become impossible to achieve a performance of the internal combustion engine, which is basically required in connection with an engine speed, a load factor and others.